Spatially discrete disturbance processes enhance grassland floral resources

Grasslands provide essential floral resources for both managed and wild
pollinators. However, grassland flowers in remaining native landscapes are
threatened due to nonnative plant invasions and alterations to historic
disturbance regimes such as fire and grazing. The potential for managed
disturbance to promote grassland floral resources remains unclear. Fire
and grazing historically occurred interactively, but uniform application
of each may be a detriment to floral resources and the pollinators
depending on them. Though fire can increase resources available to plants
and stimulate flowering, it initially destroys floral resources and may
delay flower availability. Similarly, grazing removes competitors of
flowering plants, but destroys flower heads. To address this knowledge
gap, we investigated the impacts patch-burn grazing with one and two
seasons of fire per year versus season-long grazing with no fire on floral
resources in mixed-grass prairie. In patch-burn treatments, part of each
pasture is burned each year, which focuses grazing activity due to the
high quality regrowth. We aimed to use fire to remove litter around
flowering plants while also sheltering established flower heads from
grazing pressure by directing cattle away from regenerating forbs in
unburned portions of the landscape. Over two summers, we performed weekly
flower surveys in season-long grazing and patch-burn grazing pastures. We
analyzed total seasonal floral resources, maximum floral abundance, and
seasonal species richness between treatments. Over two years, we surveyed
1,238,241 ramets of 160 species, focusing on 36 common species for
individual analysis. We found broad positive associations between
patch-burn grazing and total seasonal flower abundance, maximum flower
abundance, and species richness compared to traditional management. In
most cases, patch-burn grazing with dormant and growing season fires
produced higher floral abundance, total seasonal floral resources, and
species richness than patch-burning with dormant season fires alone,
suggesting benefits of increased levels of pyrodiversity. Synthesis and
applications: Under increasing pressure to manage for declining
pollinators, rangeland managers must consider strategies to enhance floral
resources within the context of livestock production goals. The
spatiotemporal interaction of cattle grazing and fire shows promise for
promoting floral resource abundance and diversity.